This invention relates to film structures and, more particularly, to an improvement in composite film substrates particularly suited for use as ink bearing ribbons in computer printers.
It is known in the film art to use polymeric films as base materials for carbon paper and ribbons such as typewriter ribbons. U.S. Pat. No. 3,682,764 to Findley et al., for example, teaches the preparation of a high impact ribbon having improved cut resistance. The ribbon comprises a transfer layer of a porous resin matrix containing expressible ink with a polymer film backing layer bonded to the back surface thereof by an elastomeric adhesive polymer. British Pat. No. 1,003,704 to Du Pont discloses a means for reducing excessive embossing in a polyethylene terephthalate (PET) typewriter ribbon by asymmetrical orientation of the film base. Other types of ribbons particularly suited for use in typewriters are the subject of Italian Patent Ser. No. 21734 A/72 to Sala et al. Disclosed therein is a ribbon comprising an ink-bearing polyester film base having a nylon film backing adhesively bonded thereto for improved service life.
The prior art addressed problems that are inherent in applying film technology to the preparation of ribbons suitable for use in standard typewriters. Other, more subtle problems emerge when this basic technology is applied to preparing ink-carrying ribbons suitable for high speed computer printers. In such applications it may be desirable to print characters at rates in excess of about 144,000 characters per minute (1200 lines per minute, 120 characters per line). In some types of printers more than one line, and as many as six lines, of characters can be printed simultaneously which requires a ribbon that may be 10 to 14 inches wide and capable of enduring up to about 200,000 lines of printing or more.
It has been recognized that film base typewriter ribbons, particularly those of ink-bearing polyester film with a nylon film backing, may frequently bind or stall in the ribbon handling and guiding mechanisms of high speed computer printers of the type hereinabove described. The tendency of these ribbons to bind or stall in their route from one reel to another can cause early ribbon failures from tearing or from damage caused by excessive type overwrites prior to normal ink exhaustion. Not only is great expense incurred because replacement ribbons must be kept readily available, but also because of computer use time that is lost when a printer is out of service.